The protein tyrosine phosphatases (PTPases) and the dual specific phosphatases share amino acid sequence identity, however the two families of proteins have distinct substrate specificities. The PTPases will hydrolyze phosphate from phospho-Tyr containing proteins while the dual specific phosphatases will hydrolyze phosphate from phospho-Ser/Thr and phospho-Tyr containing substrates. These two enzyme families are remarkable catalysts which have important roles in a variety of biological processes. The PTPases appear to regulate the activities of receptors such as insulin and the platelet-derived growth factor receptor. A bacterial PTPase has been shown to be a virulence determinant in the pathogenic bacteria responsible for the Plague or the Black death. The dual specific phosphatases include the cell cycle regulator, cdc25, which functions to dephosphorylate cdc2. This family of catalysts play important roles in cell growth and cell division. The dual specific phosphatases are also present in pathogenic viruses, such as vaccinia as well as in smallpox virus. One of the goals outlined in this proposal is to understand the structure and function of the PTPase. We will use kinetic, and mechanistic studies coupled with an X-ray structure (which is in progress) to develop a more complete picture of the catalytic mechanism of these proteins. The catalytic properties of invariant acidic residues (Asp, Glu), as well as invariant Arg residues present in all PTPases, will be examined. The goal is to define their role(s) in substrate binding and/or catalysis. We will also determine if the bacterial and mammalian PTPases use a common catalytic strategy. Studies on the dual specific phosphatases will focus on obtaining one member of this family in large quantities for structural and functional studies (the dual specific phosphatase we have targeted in these studies is Vaccinia H 1 Related phosphatase; VHR). Efforts will be directed at obtaining crystals suitable for an X-ray structure determination. This information will likely lead to a greater understanding of the catalytic properties of the entire family of dual specific phosphatases.